The invention relates to liquid sensing.
There are various ways to sense the level of a liquid in a tank, reservoir, or other liquid container. Some liquid level sensors use floats that have enough buoyancy to enable them to rise and fall with the surface of the liquid. Another type of liquid level sensor for small reservoirs is the thermister, which can be calibrated for use in high temperature fluids. Optical sensors, such as those that detect the difference between the index of refraction of air and liquid, can also be used.
Some liquid level sensors are point level sensors that indicate when a liquid has reached a predetermined height. Some liquid level sensors may indicate the level of a liquid over a continuous range.
The invention relates to liquid sensing.
In one aspect, the invention features a liquid sensing apparatus, including a magnetic element, a source of magnetic field, producing on the magnetic element a magnetic force with a component that opposes a gravitational force on the magnetic element, and a structure configured to prevent rotation of the magnetic moment of the magnetic element to a point where there is no longer a magnetic force component opposing a gravitational force on the magnetic element.
Embodiments may include one or more of the following features. The structure is further configured to allow liquid to contact the magnetic element. The magnetic clement is acted on by a buoyancy force of a liquid. The apparatus further includes a sensor, such as a Hall effect sensor or a reed switch, that is responsive to the position of the magnetic element. The sensor is configured to feed back a signal that is responsive to the position of the magnetic element to the source of magnetic field.
The source of magnetic field can include an electro-magnetic coil or a magnet, such as a ferromagnetic material. The magnetic element can further include a non-magnetic material, such as one surrounding the magnetic material. The non-magnetic material can have density lower than the density of the magnetic material. The non-magnetic material can include a polymer.
In another aspect, the invention features a liquid sensing apparatus including a housing, a source of magnetic field associated with the housing, a sensor associated with the housing, and a magnetic element movably located within the housing, the magnetic element being between the source of magnetic field and the sensor.
In another aspect, the invention features a liquid sensing apparatus including a structure containing a post, a source of magnetic field located at a first end of the structure, a magnetic element slidably engaged with the post, and a sensor that is responsive to the position of the magnetic element at a second end of the structure.
In another aspect, the invention features a liquid sensing method. The method includes orienting a magnetic element in a magnetic field such that there is a magnetic force with a component that opposes a gravitational force on the magnetic element, and preventing the magnetic moment of the magnetic element from rotating relative to the magnetic field so that the magnetic force remains greater than the gravitational force.
Embodiments may include one or more of the following features. The method further includes contacting liquid to the magnetic element. The magnetic element is acted on by a buoyancy force of a liquid. The method further includes sensing the position of the magnetic element. The method further includes feeding back a signal that is responsive to the position of the magnetic element to the source of magnetic field.
The magnetic field can be provided by an electromagnetic coil or a magnet, such as a ferromagnetic material. The magnetic element can further include a non-magnetic material, for example, one surrounding the magnetic material. The non-magnetic material can have density lower than the density of the magnetic material. The non-magnetic material can include a polymer.
Other aspects, features, and advantages of the invention will be apparent from the description of the preferred embodiments thereof and from the claims.